Replacing the libgraphqlparser dependency with tao::pegtl

Merge pull request #2 from Microsoft/pegtl

Replace the GraphQL parser with a PEGTL implementation

Updating to production ready

While there's still more to do and it's not ready for v1.0, I think this is ready for use in another project now. So I'm dropping the pre-release flag from this release.

This version updates the documentation and samples, plus some tweaks to the CMake configuration to make it easier to create a vcpkg port from this release.

Initial public release

See the README file for instructions on getting started on Linux or Windows.